Since thin film transistors (TFTs) have good switching characteristics, now they have been widely used in flat panel display apparatus. Typically, a thin film transistor includes a gate electrode, an active region, a source electrode and a drain electrode with the source and drain electrodes being disposed on both ends of the active region and in contact with the active region. For example, when gate voltage is higher than threshold voltage, the source electrode and the drain electrode are in electric conduction through the active region, and carriers flow from the source electrode to the drain electrode or from the drain electrode to the source electrode.
The active region of a thin film transistor usually uses ZnON (zinc nitrogen oxide) material, which, compared to IGZO (indium gallium zinc oxide) material, has nitrogen voids with relatively higher mobility during electric conduction, in this way the conduction performance of the thin film transistor can be greatly improved. In addition, since ZnON material is cheaper than IGZO material, the manufacturing cost of the thin film transistor can be greatly reduced by using ZnON material as the active region.
However, different contents of nitrogen element in ZnON material result in different mobilities, and during the period in which the thin film transistor is turned on and during the annealing process of ITO (Indium Tin Oxide) of the display substrate (e.g. an array substrate) of a display apparatus, the nitrogen element in the active region migrates to the adjacent gate insulating layer or passivation layer due to diffusion effects, which reduces the mobility of nitrogen voids in the active region, and thus increases the sub-threshold swing amplitude of the thin film transistor, the increase of the sub-threshold swing amplitude has a strong impact on the semiconductor characteristics of the thin film transistor.